Disinfectant, Biology

General information about disinfectants

A disinfectant is a chemical that kills disease-causing agents on contact. Natural disinfection agents, such as sunlight, heat, keeping poultry houses idle for a period between two batches are considered to be of limited use. All require a certain amount of contact time to be effective. Use of disinfectants at the recommended concentration is important for their effectiveness. Majority of disinfectants loose their effectiveness in the presence of organic matters. An ideal disinfectant is effective against majority of infectious agents (bacteria, parasites, viruses, fungi) and their infective stages like spores, eggs and larva etc.. They must be effective under farm conditions, organic soiling, at low temperatures and should be soluble in water including hard water. It must have a longer self-residual sanitizing and disinfecting properties and should also be safe for humans, animals as well as eco-friendly (biodegradable). It should be non- corrosive, non-toxic, non-staining and without offensive odor. Availability and cost- effectiveness are other prerequisites of an ideal disinfectant.

Based on their chemical composition, disinfectants are divided into the following classes: phenols, iodophors, quaternary ammonium compounds, alcohols, alkali, chlorine compounds, formaldehyde, chlorhexidine and oxidizing agents. A description of disinfectants which are active against most of the pathogens with their concentration and recommended use is given here.

Phenol, a chemical substance that is obtained from coal tar, is also known as carbolic acid. It is usually sold in water solutions and has a characteristic smell. It is the most commonly used and a very effective disinfectant when used at a dilution of 1:1000. Phenyl, another coal tar product, is used as 1-5% aqueous solutions for floor-mopping and dipping of vehicle's tires as well as footwear. Phenolic disinfectants are effective against bacteria (especially gram positive bacteria) and enveloped viruses, and not effective against non-enveloped viruses and spores. These disinfectants maintain their activity in the presence of organic material. Synthetic phenols (2% solution) can also be used for floor treatment.

Iodophors, iodine-containing disinfectants also with a detergent activity, are used mostly in surgical scrubs. Tincture iodine has limited cleaning ability. These compounds are bactericidal, sporicidal, virucidal and fungicidal but require a prolonged contact time. The disinfective ability of iodine, like chlorine, is neutralized in the presence of organic material and hence frequent applications are needed for thorough disinfection. Iodine tinctures can be very irritating to tissues, may stain surfaces and tissues brown and are corrosive.

The quaternary ammonium compounds are widely used as disinfectants but are contra indicated as antiseptics. They are forms of ammonium chloride with benzyl, dimethyl, ethyl-benzyl or similar combination. These disinfectants are effective against Gram positive and Gram negative bacteria, and enveloped viruses but not against non-enveloped viruses, fungi and bacterial spores. Quaternary ammonium salts @ 4% solution used for treatment of walls, floors, ceilings and equipment also.

Alcohol is available as water-soluble chemicals in form of ethyl alcohol, isopropyl alcohol and rectified spirit, which are rapidly bactericidal, fungicidal, and virucidal against enveloped viruses. These are not effective against bacterial spores and have limited effectiveness against non-enveloped viruses. Their antimicrobial activity can be attributed to their ability to denature proteins. Higher concentrations are less effective as the action of denaturing proteins is inhibited without the presence of water; hence 60-90% aqueous solutions are more effective. Alcohols are commonly used as topical antiseptics. They are also used to disinfect the surface and equipment. Alcohols require time to work and they may not penetrate organic material.

All acids and alkalis have disinfectant properties but are corrosive and hence lead to tissue damaging effects. Peracetic or peroxyacetic acid have a very rapid action against all microorganisms. A special advantage of peracetic acid is that it has no harmful decomposition products and leaves no residue. It remains effective in the presence of organic matter and is sporicidal even at low temperatures. Sodium hydroxide is an effective agent and used most commonly as 2% solution at the entrance on foot mats to clean the shoes and this solution can also be used to scrub and clean gumboots and other items. The formic acid has been safely used in animal and poultry feeds to prevent mycotoxic effects. Lime (calcium hydroxide) is commonly used as 3% solution to disinfect the walls, litter, floor and also the poultry carcasses while dumping under ground. It is mainly used in areas that are damp and cannot be exposed to the sun, as well as for disinfection of drains, fecal matter and for white wash. The action of lime depends on liberation of heat and oxygen when the chemical comes in contact with water. Heat destroys bacteria and parasitic eggs and even coccidia, and keeps fungi under control. Cresolic acid 2.2% solution can be used for treatment of floors.

Hypochlorites are the most widely used of the chlorine disinfectants and are available in a liquid e.g. sodium hypochlorite (bleach) or solid e.g. calcium hypochlorite. Bleaches are very harsh but effective. They attack pathogens, organic debris and living tissues equally well. Bleach can create toxic fumes which can lead to chemical pneumonia, skin and eye irritation or burns. Bleach is inexpensive and easily available without a license. Depending on the concentration at which it is mixed it can kill most bacteria, viruses and Mycoplasma but not spores. Hypochlorite can eliminate both enveloped and non-enveloped viruses if used in correct dilution and contact time. Household bleach is typically diluted using 1:50 with water (1,000 ppm) for surface disinfection. It is a potent deodorizer and works best in the presence of sunlight which releases more free radicals. It is very caustic to tissues and equipment but very rapidly inactivated by organic debris. Sodium hypochlorite (2% active chlorine solution) is used for disinfection of equipments.

Formaldehyde, a gaseous disinfectant, is sold commercially in a 40% aqueous solution as formalin. Formalin is the most effective disinfectant, cheap and easily available. It is used for fumigation of poultry house, brooder, and hatchery. Formaldehyde is usually generated by adding formalin to potassium permanganate in an earthen pot. About 60-70 g of potassium permanganate mixed with 120-150 ml of formalin is sufficient for disinfecting 100 cubic feet of space. Gas should be allowed to remain for 1-6 h in the rooms, incubators, brooders, etc. For disposal of infected material including dead birds, a 10% solution of formalin is an ideal disinfectant but it should be used under technical guidance.

Peroxides such as hydrogen peroxide (6% solution) are often used as antiseptics to clean wounds. The activity of peroxides is greatest against anaerobic bacteria. Hydrogen peroxide at high concentrations is in some cases is damaging to tissues.

Conventional sterilization entities i.e. flame and steam are best suited for poultry operations. Flame is an excellent cleaner and sanitizer. Gas torches will kill any known living organism. Post-outbreak cleaning is best achieved by burning down cages and other poultry equipments that are heat and flame resistant. Battery cages and pen walls are sterilized using flame gun. All the litter, contaminated feed and carcasses are burnt completely to ashes. Incinerators (electrical or furnace oil) can also be installed considering its capacity requirement. However, flame has limitations in several aspects. Pressurized steam directed into cracks and corners is an excellent sterilizing material. It could be costly and may not be convenient to open areas.